The present invention relates to an on die thermal sensor (ODTS), an integrated circuit having the same, and an on die thermal sensing method.
An integrated circuit, for example, a unit cell of a dynamic random access memory (DRAM), includes a transistor and a capacitor. It is determined whether data is stored or not according to whether electric charge is stored in the capacitor or not, that is, according to a terminal voltage of the capacitor. Here, data stored in a unit cell is erased by the unintended loss of electric charge in the capacitor. In order to prevent the unintended data loss, data stored in a unit cell is checked before losing the electric charge in the capacitor and the electric charge is re-charged to a normal level. Such a re-charge process is referred as a refresh operation. The refresh operation is classified into an auto refresh operation and a self refresh operation. The auto refresh operation and the self refresh operation are identical in a view that an address is internally generated in the refresh operation. However, the auto refresh operation and the self refresh operation are different in a refresh cycle, an operation time, and whether it is driven by an external command or not.
The auto refresh operation is performed by an auto refresh instruction (AREF) that is applied at a cycle of several tens ns from an external controller. The self refresh operation is performed by a self refresh start instruction SREF and a self refresh end instruction SREX, which are applied at a cycle of several μs. The cycle of the auto refresh operation is shorter than the cycle of the self refresh operation. The refresh operation is controlled by a controller of an integrated circuit. An integrated circuit consumes a refresh current for performing the refresh operation. Such power consumption for the refresh operation is a very important issue for devices that are driven using a battery.
In order to reduce the power consumption for the refresh operation, the refresh cycle is changed according to a temperature. The lower an internal temperature of an integrated circuit is, the longer a retention time of the integrated circuit becomes. The retention time is duration for normally detecting data before the data is erased. If an internal temperature is low, the power consumption for the refresh operation is reduced because the refresh operation is less frequently performed. Therefore, an on die thermal sensor (ODTS) for sensing an internal temperature is required to decrease the power consumption for the refresh operation.
Meanwhile, the integrated circuit generates more heat according to the increment of an integration level or the increment of the operation speed. Such heat may increase the internal temperature of the integrated circuit and cause an operation error. Therefore, it is necessary to have the ODTS in order to prevent the increment of the internal temperature and the operation error.
FIG. 1 is a diagram illustrating an ODTS according to the related art.
As shown in FIG. 1, the ODTS according to the related art includes a temperature information voltage generator 101, an analog-to-digital converter (ADC) 103, a code convertor 105, and a temperature measurement operation controller 107.
The temperature voltage generator 101 senses an internal temperature of an integrated circuit and generates a temperature information voltage VTEMP in inverse proportion to the sensed temperature.
Also, the temperature information voltage generator 101 generates a maximum voltage variation VULIMIT and a minimum voltage variation VLLIMIT for defining a maximum value and a minimum value for allowing a digital code generated by the ADC 103 according to the variation of the internal temperature of the integrated circuit. The maximum voltage variation VULIMIT and the minimum voltage variation VLLIMIT are voltages not influenced by process, voltage, and temperature (PVT). The maximum voltage variation VUMLIT and the minimum voltage variation VLLIMIT can be set to a predetermined level using a virtual fuse code and a trim code inputted from the temperature information voltage generator 101.
The ADC 103 converts a temperature voltage to a digital code and outputs the digital code. In order to control the minimum voltage variation and the maximum voltage variation VLLIMIT and VULIMIT, the digital code is feedback to the temperature information voltage generator 101.
The code convertor 105 converts the digital code from the ADC 103 to a temp code and a plurality of trip point flags.
For example, the trip point flags are a plurality of flag signals each having different logical level according to an internal temperature of an integrated temperature. For example, flag signals TEMP A, TEMP B, and TEMP C are generated. The plurality of generated flag signals TEMP A, TEMP B, and TEMP C are used to control the cycle of the self refresh operation.
The temperature measurement operation controller 107 controls the ODTS operating in a normal mode based on an enable signal ENABLE inputted from the outside. The temperature measurement operation controller 107 also control the ODTS operation in a self refresh mode based on a self refresh signal SREF inputted from the outside. The temperature measurement operation controller 107 controls the operation of the temperature information output device by deciding a control signal BGR_ON for controlling the operation of the temperature information voltage generator 101 and a control signal ADC_ON for controlling the operation of the ADC 103.
A multipurpose register (MPR) 109 is disposed outside the ODTS and stores the latest temp code generated by the code converter 105. The MPR 109 outputs predetermined information instead of cell data. For example, the MPR 109 defines a predefined pattern [01010101] and a temp code that is internal temperature information of an integrated circuit as predetermined information.
A self refresh oscillator 111 perform an auto self refresh (ASR) operation in a self refresh mode of an integrated circuit and controls a cycle of the self refresh operation in response to a plurality of flag signals TRIP POINT FLAG outputted from the code converter 105. The ASR controls a cycle of a self refresh operation according to an internal temperature of an integrated circuit while performing the self refresh operation. That is, the ASR minimizes unnecessary quiescent current. Meanwhile, the higher the internal temperature of the integrated circuit is the greater the leakage current becomes in the unit cell. Therefore, the retention time becomes shorted. The ASR prevents data from being lost through frequent refresh operations by controlling the cycle of the self refresh operation shorter if the internal temperature of the integrated circuit increases.
FIG. 2 is a diagram illustrating an analog digital converter of FIG. 1.
As shown in FIG. 2, the ADC 103 includes a comparator 201, an up-down counter 203, a decoder 205, and a digital to analog converter (DAC) 207.
The comparator 201 compares a temperature voltage generated by the temperature information voltage generator 101 with a tracking voltage DACOUT. If a potential level of the temperature voltage VTEMP is smaller than that of the tracking voltage DACOUT, an increment signal INC is activated. If a potential level of the temperature voltage VTEMP is larger than that of the tracking voltage DACOUT, a decrement signal DEC is activated.
The up-down counter 203 generates an up counted digital code based on, for example, the increment signal INC activated by the comparator 201. The up down counter 203 also generates a down-counted digital code based on the decrement signal activated by the comparator 201.
The comparator 201 and the up down counter 203 operate at a predetermined time interval DEALY in response to the sample clock SampleCLK.
The decoder 205 converts the digital code up-down counted by the up down counter 203 to the temperature information code THERMOTHER CODE.
The DAC 207 converts the thermometer code generated from the decoder 205 to a tracing voltage DACOUT. Here, the tracking voltage DACOUT variation range is from the minimum voltage variation VLLIMIT to the maximum voltage variation VUMLIMIT.
Related to the MPR, a function of outputting the internal temperature information of the integrated circuit is rarely used. Therefore, if the rarely used internal temperature information outputting function is removed from the integrated circuit, it is not necessary for the ODTS to output TEMP code, which is an internal temperature of the integrated circuit. Therefore, if the internal temperature information output function is removed, it is not necessary to have the temperature information voltage generator 101 and the ADC 103 which occupy a large layout area
In this case, it is necessary to reconfigure the ODTS according to the related art to be suitable for ASR instead of the temp code.